The present invention relates to an open capillary column which may be provided for a separation analysis field such as liquid chromatography and electrochromatography, and manufacturing method thereof.
In a conventional open capillary column, it is rare that an excellent chromatogram is obtained under a reversed-phase condition of a chemical-modification type open capillary column in liquid chromatography and, simultaneously, the relative retention value is equal to or larger than 0.5 under condition of a 50% methanol solution. The relative retention is determined by the size of the surface area of a stationary phase and the thickness of the phase. However, since the thickness of the stationary phase relates to a mass transfer coefficient, if the stationary phase is too thick, a chromatogram displaying excellent separation is not obtained. Consequently, development of a stationary phase having a large surface area is not so advanced.
As columns for electrochromatography, there are three columns of a packed-type capillary column, a loosely packed column, and an open capillary column. In the electrochromatography, a voltage is applied in the column axis direction. Consequently, a current flows in the column and Joule""s heat is generated. Bubbles may be generated in the column due to the Joule""s heat. In the case where bubbles are generated, the operation has to be stopped once to remove the bubbles from the column. To solve the problem of bubbles, another problem arises from the viewpoint of operation such that the column has to be washed with high voltage of the liquid chromatography. Ease of the removing operation is the key to obtain a stable operation of electrochromatography. Therefore, it is the most effective to employ an open capillary column as a column for electrochromatography.
Conventionally, as a material of a glass capillary tube, soda glass is used. A chemical treatment on the surface of glass is easy, and an excellent silica stationary phase is realized by deposition of silica which occurs simultaneously with fusion of the glass surface by sodium hydroxide solution. However, soda glass is brittle and easily bent, so it is not suitable for wide use. At present, fused silica capillary glass is widely employed as very stable glass. However, the glass surface of the material is very stable, and it is very difficult to enlarge the surface area by chemical treatment. Although the surface of the fused silica capillary glass may be etched by a treatment at high temperature (for example, 350xc2x0 C. to 400xc2x0 C.) with an ammonium bifluoride reagent, an excellent column has not been achieved yet by the method. A surface treatment under severe conditions is accompanied by deterioration of a column in the long term.
There is a case that a column developed as a stationary phase extracting tube for gas chromatography is properly cut to be short and the resultant is used for collecting samples. Inherently, in the case of dealing with a sample of liquid or solution, a sample collection tube developed for liquid is desirable. When an open capillary tube is used as a sample collection tube, the flow resistance is low at the time of collecting samples and sampling operation may be easily performed. An open capillary tube, that is, a short capillary column in which a stationary phase of a large sample addition amount provided for this purpose is formed is desired. However, a material having proper functions of such an open capillary tube does not exist yet.
An object of the present invention is therefore to provide a column in which a stationary phase having a very large surface area is formed as an open capillary column provided for a separation analysis field such as liquid chromatography and electrochromatography and to provide a method of manufacturing the column.
In an open capillary column of the present invention, a stationary phase is formed on the inner wall of an open capillary tube. The stationary phase comprises a number of pores on the surface, and each of pore has an expanded hollow in the stationary phase.
In the present invention, the open capillary tube may be a fused silica capillary tube.
Further, the open capillary tube may be obtained by cutting an open capillary tube material with an arbitrary proper length.
In the present invention, as a base material of the stationary phase, oligo silica, oligo zirconia or oligo titania may be used.
Further, the stationary phase may be chemically modified stationary phase by adding chemically modification. Specifically, the surface of the stationary phase and/or the expanded hollows in the stationary phase may be subjected to chemical modification, thereby obtaining a chemically modified stationary phase. In this case, the surface of the stationary phase and the expanded hollows in the stationary phase may be subjected to different chemical modifications, thereby obtaining a chemically modified stationary phase.
In the present invention, as a functional group of chemical modification, any of alkyl group, xcex3-aminopropyl group, cyanoethyl group, cyclodextrin group, and ion exchange group may be selected.
In an open capillary column of the present invention, the inner wall of the open capillary tube is subjected to alkaline treatment. Subsequently, oligo silica, oligo zirconia, or oligo titania is applied on the inner wall, and the open capillary tube is filled with an alkaline solution to form a silica layer, a zirconia layer, or a titania layer. The alkaline solution is discharged and, after that, the capillary tube is subjected to heat treatment, thereby forming a base of a stationary phase.
The above and other objects and effects of the invention will become apparent in the following description with reference to the accompanying drawings.